MANILA - As many as 10,000 people are feared dead in one city alone after Super Typhoon Haiyan - one of the most powerful storms ever recorded - slammed into the central islands of the Philippines, officials said.

Regional police chief Elmer Soria said he was briefed by Leyte provincial Gov. Dominic Petilla late Saturday and told there were about 10,000 deaths on the island, mostly by drowning and from collapsed buildings. The governor's figure was based on reports from village officials in areas where Typhoon Haiyan slammed Friday.

Tacloban city administrator Tecson Lim said that the death toll in the city "could go up to 10,000." A mass burial was planned Sunday in Palo town near Tacloban.

Interior Secretary Mar Roxas said a massive rescue operation was underway. "We expect a very high number of fatalities as well as injured," Roxas said after visiting Tacloban on Saturday.

On Samar Island, which is facing Tacloban, Leo Dacaynos of the provincial disaster office said Sunday that 300 people were confirmed dead in Basey town and another 2,000 are missing.

He said that the storm surge caused sea waters to rise 20 feet when Typhoon Haiyan hit Friday, before crossing to Tacloban.

There are still other towns on Samar that have not been reached, he said, and appealed for food and water. Power was knocked out and there was no cellphone signal, making communication possible only by radio.

Reports from the other four islands were still coming in, so far with dozens of fatalities.

If the typhoon death toll is confirmed, it would be the deadliest natural catastrophe on record in the Philippines. The deadliest typhoon before Haiyan was Tropical Storm Thelma in November 1991, which killed around 5,100 people in the central Philippines. The deadliest disaster so far was the 1976 magnitude-7.9 earthquake that triggered a tsunami in the Moro Gulf in the southern Philippines, killing 5,791 people.

The storm weakened Sunday to 103 mph with stronger gusts and was forecast to loose strength further when it hits northern Vietnam's Thanh Hoa province early Monday morning.

As Haiyan heads west toward Vietnam, the Red Cross is at the forefront of an international effort to provide food, water, shelter and other relief to the hundreds of thousands of residents who have lost their homes and livelihood, Gordon said.

"This is a big, full-court press," he said. "We're pulling out all the stops to help."

With widespread power outages, roads blocked, bridges down and debris strewn everywhere, getting life back to some semblance of normal in the region will take time.

"The Philippines are always resilient, and we're going to get back up," Gordon said.

Anna Lindenfors, Philippines director of Save the Children, said officials in the country were still trying to gather information about the damage caused by Typhoon Haiyan. As of Saturday, communication lines to the hardest-hit areas had yet to be re-established, she said.

"With this magnitude, we know that the destruction is overwhelming," said Emma Amores, who was waiting outside Villamor Airbase in Manila, where a C-130 was loading relief supplies and personnel heading to hard-hit Tacloban. "From the images we saw on TV, it's highly likely our houses are gone. We just want to know that the family are all safe."

Romil Elinsuv, who is in Manila for work training, worried about his wife and 4-year-old son, who are at their home in Palo, a town in the province of Leyte.

"I feel fear. I don't know what the situation is there," Elinsuv said. He said he spoke with his wife the day before. She assured him they were OK, but then the line went dead, and he's been unable to reach her since.

Super Typhoon Haiyan hit Guiuan, on the Philippine island of Samar, at 4:40 a.m. local time Friday. Three hours before landfall, the Joint Typhoon Warning Center assessed Haiyan's sustained winds at 195 mph, gusting to 235 mph, making it the fourth-strongest tropical cyclone in world history.

Graciano Lopez, 65, of Midlothian, Va., spent much of Friday night and Saturday morning glued to his television, phone and Facebook account waiting for word from family members in the Philippines. A retired engineer, Lopez grew up in Quezon City just outside of Manila. Throughout his childhood, he lived through various typhoons, the damage they leave behind and the rebuilding process that often meant annually replacing roofs of homes.

But this weekend, Lopez knew Haiyan was not like any typhoon he had experienced. He took pains to warn family members in the Philippines to be ready for the worse. "I was worried," he said. "I knew this was in a different league."

Lopez's relatives were spared the brunt of the storm and were left dealing with roofs that had been blown off and downed trees, he said.

"They are very thankful," Lopez said. "They got ordinary storm damage which they get several times a year so they were all kind of ready for that."

After losing strength as it moved over the Philippines and west into the South China Sea on Saturday, Haiyan was expected to maintain typhoon strength and hit Hanoi, Vietnam, late Sunday local time.

Preparations were well underway in the country Saturday ahead of the storm, with nearly 500,000 having been evacuated from high-risk areas across the central region from Phu Yen to Quang Binh provinces, according to state-run local media.

Witnesses in Danang reported empty supermarket shelves by Friday as anxious locals rushed to stock up on supplies in anticipation of the deadly typhoon's arrival.

The typhoon is expected to hit Vietnam as a Category 2 or 3 typhoon according to the Red Cross, which estimates 6.5 million people will be affected by the storm.

The storm has already claimed its first victims in Vietnam, with local media reporting two people dead and 30 more injured in Quang Nam province Friday as a result of accidents during storm preparations.